Air hardening steel



Patented Oct. 9, 1934 UNITED STATES PATENT OFFICE AIR HARDENING STEEL Herbert Han-is, Milwaukee, Wis., assignor to A.

0. Smith Corporation, Milwaukee, Wis., a cor- No Drawing.

Serial No. 619,532

4 Claims.

The invention relates to alloys which are composed mainly of iron with small amounts of copper, manganese and carbon.

It is among the objects of the invention to pro- 5 vide alloys which can be relatively easily worked by forging, rolling and the like, and can be given great strength, hardness and toughness by heating to predetermined temperatures and mildly quenching, as by cooling in air.

Another object of the invention is to provide for improving the workability of the described alloy without destroying its air hardening properties.

I have made low carbon steels containing about 3.0% to 4.0% copper, 1.5% to 2.0% manganese and 0.1% to 0.25% carbon. It was found that the steels developed a remarkably strong, tough, martensitic structure by cooling in still air from above the critical point,- say about 800 C. to 850 C.

For example, in the air quenched condition, an alloy composed of 4.0% copper, 2.0% manganese, 0.16% carbon and the remainder iron with small amounts of impurities was found to have an elastic limit of 150,000 pounds per square inch, ultimate strength of 190,000 pounds per square inch, an elongation of 13.5% in two inches and a Brinell hardness of about 380 to 400. By quenching from about 800 C. in oil the ultimate strength was about 200,000 to 210,000 pounds per square inch.

Lower copper and carbon give lower strengths and the steels are not suitable for uses where great strength is required. With higher carbon contents, brittleness is developed while with higher copper thesteel becomes practically unworkable. Some of the best results are obtained with about 0.15% carbon. With both the copper and manganese within the described limits, hardness is developed by air cooling, but without the copper only a soft steel is produced. The air hardening properties are lost when the manganese is reduced below the described limits. In making these steels, care should be taken to avoid oxidation since the presence of iron oxide in steel tends to cause hot shortness.

The alloys are easier to forge and roll and the air hardening property of the alloy is improved by substituting chromium for a part of the manganese. Small amounts of chromium are effective and amounts up to about 0.5% can be used. An inclination to brittleness without material effect on the strength is produced by excessive amounts of chromium.

'Ihe alloys can be readily rolled, forged and worked. Without employing costly heat treatment which is necessary in the standard practice of manufacturing carbon steel articles, exceptional strength can be obtained with the alloys. The cost of manufacturing the alloys is relatively low since these constituents are among the more abundant alloy elements and the loss of the alloy elements in manufacturing is not great. By quenching, I provide finished articles at relatively low cost which articles are by far harder, stronger and more ductile than the carbon steels and which compare favorably with the special alloys that are costly to manufacture.

I claim:

1. An alloy composed of about 3.0% to 4.0% copper, about 0.1% to 0.25% carbon, about 1.5% to 2.0% manganese, and a substantial addition of chromium but not more than about 0.5%, the chromium being substituted for an approximately equal amount of manganese, the balance of the alloy being substantially all iron.

2. An alloy composed of about 4.0% copper, 0.16% carbon, and 2.0% manganese, the balance being substantially all iron.

3. An air quenched article of alloy steel composed of about 3.0% to 4.0% copper, about 0.1% to 0.25% carbon, and about 1.5% to'2.0% manganese, the balance being substantially all iron, said article having an ultimate strength of at least 190,000 pounds per square inch and an 85 elongation in two inches of about 13.5%, developed by heating the steel to above its critical point and cooling in air.

4. An air quenched article of alloy steel composed of about 4% copper, 0.16% carbon, and

'2.0% manganese, the balance being substantially all iron, said article having an ultimate strength of about 190,000 pounds per square inch and an elongation in two inches of about 13.5%, developed by heating the steel to above its critical point and coolingin air.

HERBERT HARRIS. 

